The invention relates generally to power plants producing electricity from coal or other solid or low grade liquid fuels and more specifically to an integrated gasification power plant including a fuel cell and a steam turbine power plant.
A variety of different systems have been used to generate electrical power from coal and low grade fuels. One such system is an integrated gasification gas turbine combined cycle power plant (IGCC). In this system a conventional gas turbine combined cycle power plant utilizes combustion of the gasified fuel to induce rotation of gas turbine blades coupled to a shaft that is coupled to a generator. The generator converts the rotational energy produced by the turbine into electrical energy. The fuel for combustion in the turbine may be provided by a gasifier, which produces a gaseous fuel from a solid fuel, such as coal or other solid or low grade liquid fuels (e.g. biomass, heavy oils). The exhaust waste heat can be recovered in a bottoming steam turbine system.
In addition, fuel cells have been integrated with conventional gas turbines to improve the efficiency of the power plant. Fuel cells typically cause a reaction between a fuel, such as hydrogen, and an oxidant, such as air, which produces electrical power. The fuel cells also produce hot gases that may be mixed with the fuel for combustion in the gas turbine, which improves the efficiency of the system. In addition, integration of a fuel cell into a conventional IGCC plant is a possibility.
However, all these types of power plants have several disadvantages. For example, a typical gasifier combined cycle power plant has a low thermal efficiency, approximately 40 percent. Furthermore, there may be a large amount of carbon dioxide produced by the gasifier in addition to the fuel. However, removing the carbon dioxide from the fuel before the fuel is combusted in order to reduce carbon dioxide emissions significantly reduces the performance of the system. Furthermore, the fuel cells that are used in such plants do not consume all of the fuel that is fed into the fuel cell, thereby reducing the efficiency of the system.
Therefore, it is desirable to provide a power plant with greater efficiency and with reduced emissions. The techniques described below may provide a solution to one or more of the problems described above.